This invention relates to a trailer coupling and in particular to a latch which prevents a trailer coupling from becoming opened inadvertently.
Trailer couplings of the type which have a vertical pintle that receive the annular eye of a trailer drawbar generally have a multiple-stage locking mechanism which prevents the latch from becoming lifted in use and thus permit the drawbar to accidentally lift off of the pintle. Until recently devices of this type were at best double locking; that is two independent motions had to be made in order to release the latch mechanism so that it could be lifted off of the pintle. Typical of double locking couplings are Weiss, U.S. Pat. No. 3,475,037, Weiss, U.S. Pat. No. 2,842,380 and Weiss, U.S. Pat. No. 2,766,995. Recently triple locking latches have become known which provide a greater degree of safety against accidental release of the drawbar than is obtained with double locking latches. Couplings having triple locking latches are manufactured and sold by Eagle Manufacturing Company of Portland, Oreg. and are designated as the 600 Series.
The primary advantage of the Weiss '037 coupling over the earlier Weiss '380 coupling is that the latter coupling requires lateral sliding movement of one of the locking elements to unlock it, whereas the former coupling utilizes rotary movement to unlock all of its locking components. While sliding generally works well, when the locking mechanism is not activated for a period of time rust can accumulate and cause a sliding element to bind. Even though the Eagle 600 Series couplings provide the superior safety of triple locking, they utilize sliding as the method of releasing one of their locking elements and thus are susceptible to becomming jammed due to rust. In addition, the three locking mechanisms in the Eagle 600 Series couplings are not totally independent, and the failure of certain elements in one of the locking mechanisms will make another of the locking elements inoperative.
The present invention provides a triple locking trailer coupling which overcomes the shortcomings of the prior art triple locking couplings by providing entirely rotary locking elements. The latch which contacts the extremity of the pintle that carries the trailer drawbar is locked in place by means of a rotatable pawl which must be lifted off of the latch before the latch can be raised. The pawl rotates on a shorter radius than the latch does and when in contact with the latch it interferes with a raised block on the latch to prevent an attempt to rotate the two elements together. Thus, the latch cannot be rotated away from the pintle without first lifting the pawl away from it.
Located medially in the rear of the pawl is a cavity which has a pair of elongate, rectangularly cross-sectioned prongs rotatably mounted in it. The prongs are positioned so that their forwardmost ends are always located inside of the cavity and they can be rotated so that the remainder of their extent either is located entirely in the cavity or else projects from it. A spring located between the prongs urges them toward the position where they extend out of the cavity.
The walls of the hitch body have notches in them which permit the prongs to protrude out of the cavity in the pawl when the pawl is in its locked position on top of the latch. The notches are localized and thus contact the tops of the prongs so as to prevent the pawl from being raised. As a result it is necessary to deflect the prongs against the spring before the pawl can be lifted off of the latch.
A cam, which is mounted rotatably on the bolt which journals the pawl, has paired plates which fit behind the rearward ends of the prongs. The plates are arranged so that when the cam is rotated to a locked position they lie behind the prongs and prevent them from being deflected into the cavity, and when the cam is rotated to an unlocked position they are positioned away from the prongs. A spring simultaneously urges the cam to its locked position and the pawl down against the latch.
Accordingly, in order to raise the latch it is necessary to first rotate the cam against the spring to its unlocked position. Then, while the cam is being held in its unlocked position, it is necessary to deflect the prongs into the cavity in the pawl. Finally, while the prongs are still being deflected, it is necessary to lift the pawl away from the latch.
Not only are three independent rotary steps required to unlock the latch, incapacitation of either of the elements which provide the first two steps will not disenable the locking mechanism but the remaining lock elements will remain in effect and must be released in order to lift the latch.
Accordingly, it is principal object of the present invention to provide a locking mechanism for trailer couplings which requires three independent locks to be opened in order for the latch to be made openable.
It is a further object of the present invention to provide such a locking mechanism where all three locks are activated by rotary movement.
If is a further object of the present invention to provide such a locking mechanism where faillure of either of the first two locks does not prevent the remaining two from operating.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.